title: Phosphocreatine recovery kinetics following low- and high-intensity exercise in human triceps surae and rat posterior hindlimb muscles.
abstract: Previous studies have suggested the recovery of phosphocreatine (PCr) after exercise is at least second-order in some conditions. Possible explanations for higher-order PCr recovery kinetics include heterogeneity of oxidative capacity among skeletal muscle fibers and ATP production via glycolysis contributing to PCr resynthesis. Ten human subjects (28 +/- 3 yr; mean +/- SE) performed gated plantar flexion exercise bouts consisting of one contraction every 3 s for 90 s (low-intensity) and three contractions every 3 s for 30 s (high-intensity). In a parallel gated study, the sciatic nerve of 15 adult male Sprague-Dawley rats was electrically stimulated at 0.75 Hz for 5.7 min (low intensity) or 5 Hz for 2.1 min (high intensity) to produce isometric contractions of the posterior hindlimb muscles. [(31)P]-MRS was used to measure relative [PCr] changes, and nonnegative least-squares analysis was utilized to resolve the number and magnitude of exponential components of PCr recovery. Following low-intensity exercise, PCr recovered in a monoexponential pattern in humans, but a higher-order pattern was typically observed in rats. Following high-intensity exercise, higher-order PCr recovery kinetics were observed in both humans and rats with an initial fast component (tau < 15 s) resolved in the majority of humans (6/10) and rats (5/8). These findings suggest that heterogeneity of oxidative capacity among skeletal muscle fibers contributes to a higher-order pattern of PCr recovery in rat hindlimb muscles but not in human triceps surae muscles. In addition, the observation of a fast component following high-intensity exercise is consistent with the notion that glycolytic ATP production contributes to PCr resynthesis during the initial stage of recovery.
authors.affiliation: Dept. of Physiology 2201 BPS Bldg., Michigan State Univ., East Lansing, MI 48824, USA.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Forbes
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Paganini
authors.forename: Jill M
authors.initials: JM
authors.lastname: Slade
authors.forename: Theodore F
authors.initials: TF
authors.lastname: Towse
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Meyer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D000818:Animals; D004558:Electric Stimulation; D015444:Exercise; D005260:Female; D006019:Glycolysis; D006614:Hindlimb; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016018:Least-Squares Analysis; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000294:innervation / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D010725:Phosphocreatine / Q000378:metabolism*; D010759:Phosphorus Isotopes; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000502:physiology
chemical_list: D010759:Phosphorus Isotopes; D010725:Phosphocreatine; D000255:Adenosine Triphosphate